test: clean up system-test setup against emulator (#319)

* test: change system-test setup against emulator

Use Docker image instead of manually downloading the emulator binary and
running it.

* chore: cleanup unusued script file

* fix: use latest version of docker image

.github/workflows/integration-tests-against-emulator.yaml

@@ -7,13 +7,23 @@ name: integration-tests-against-emulator
 jobs:
   units:
     runs-on: ubuntu-latest
+
+    services:
+      emulator:
+        image: gcr.io/cloud-spanner-emulator/emulator:latest
+        ports:
+          - 9010:9010
+          - 9020:9020
+
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-java@v1
       with:
         java-version: 8
     - run: java -version
     - run: .kokoro/build.sh
-    - run: sh .github/workflows/integration-tests-against-emulator.sh
+    - run: mvn -B -Dspanner.testenv.instance="" -Penable-integration-tests -DtrimStackTrace=false -Dclirr.skip=true -Denforcer.skip=true -fae verify
       env:
         JOB_TYPE: test
+        SPANNER_EMULATOR_HOST: localhost:9010
+        GOOGLE_CLOUD_PROJECT: emulator-test-project